The magic jar spell enables the caster to shift his life force into a special receptacle (a gem or large crystal). From there the caster can force an exchange of life forces between the receptacle and another creature, thus enabling the wizard to take over and control the body of another creature, while the life force of the host is confined in the receptacle. The special life force receptacle must be within spell range of the wizard's body at the time of spellcasting. The wizard's life force shifts into the receptacle in the round in which the casting is completed, allowing no other actions.
While in the magic jar, the caster can sense and attack any life force within a 10-footper- level radius (on the same plane); however, the exact creature types and relative physical positions cannot be determined. In a group of life forces, the caster can sense a difference of four or more levels/Hit Dice and can determine whether a life force is positive or negative energy.
For example, if two 10th-level fighters are attacking a hill giant and four ogres, the caster could determine that there are three stronger and four weaker life forces within range, all with positive life energy. The caster could try to take over either a stronger or a weaker creature, but he has no control over exactly which creature is attacked.
An attempt to take over a host body requires a full round. It is blocked by a protection from evil spell or similar ward. It is successful only if the subject fails a saving throw vs. spell with a special modifier (see following). The saving throw is modified by subtracting the combined Intelligence and Wisdom scores of the target from those of the wizard
(Intelligence and Hit Dice in nonhuman or nonhumanoid creatures). This modifier is added to (or subtracted from) the die roll. (See book for table ).